Abstract
Abstract. The Aura Tropospheric Emission Spectrometer (TES) is collecting closely spaced observations over 19 megacities. The objective is to obtain measurements that will lead to better understanding of the processes affecting air quality in and around these cities, and to better estimates of the seasonal and interannual variability. We explore the TES measurements of ozone, ammonia, methanol and formic acid collected around the Mexico City metropolitan area (MCMA) and in the vicinity of Lagos (Nigeria). The TES data exhibit seasonal signals that are correlated with Atmospheric Infrared Sounder (AIRS) CO and Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD), with in situ measurements in the MCMA and with Goddard Earth Observing System (GEOS)-Chem model output in the Lagos area. TES was able to detect an extreme pollution event in the MCMA on 9 April 2013, which is also evident in the in situ data. TES data also show that biomass burning has a greater impact south of the city than in the caldera where Mexico City is located. TES measured enhanced values of the four species over the Gulf of Guinea south of Lagos. Since it observes many cities from the same platform with the same instrument and applies the same retrieval algorithms, TES data provide a very useful tool for easily comparing air quality measures of two or more cities. We compare the data from the MCMA and Lagos, and show that, while the MCMA has occasional extreme pollution events, Lagos consistently has higher levels of these trace gases.
Highlights
The world’s megacities, defined as urban agglomerations with a population over 10 million (UN, 2016), currently house close to 500 million people, about one-eighth of the global urban population (UN, 2014)
We use in situ measurements and back trajectories to assess the influence of biomass burning on the air quality within the cities themselves, and we demonstrate the use of the Tropospheric Emission Spectrometer (TES) observations to provide finer-scale information beyond that derived from chemical transport models in these regions
The TES megacity dataset covers the period from January 2013 to present and provides air quality data over 19 metropolitan areas
Summary
The world’s megacities, defined as urban agglomerations with a population over 10 million (UN, 2016), currently house close to 500 million people, about one-eighth of the global urban population (UN, 2014). TES methanol (CH3OH) data were used to optimize GEOS-Chem methanol emission, leading to better agreement between the model and aircraft measurements (Wells et al, 2014), obtained from a number of campaigns, including MILAGRO (Singh et al, 2009), INTEXB (Singh et al, 2009), the second Texas Air Quality Study (TexAQS-II; Parrish et al, 2009) and the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS; Jacob et al, 2010).
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